In continuous ink jet printing, ink is supplied under pressure to a manifold that distributes the ink to a plurality of orifices, typically arranged in linear array(s). The ink is expelled from the orifices in jets which break up due to surface tension in the ink into droplet streams. Ink jet printing is accomplished with these droplet streams by selectively charging and deflecting some droplets from their normal trajectories. The deflected or undeflected droplets are caught and re-circulated and the others are allowed to impinge on a printing surface.
Drops are charged by a charge plate having a plurality of charging electrodes along one edge, and a corresponding plurality of connecting leads along one surface. The edge of the charge plate having the charging electrodes is placed in close proximity to the break off point of the ink jet filaments, and charges applied to the leads to induce charges in the drops as they break off from the filaments. U.S. Pat. No. 5,512,117, issued Apr. 30, 1996 to Morris, describes one method of fabricating a charge plate. The charge plate taught by Morris is fabricated by electro-depositing the charging electrodes and leads on a flat sheet of etchable material, such as copper foil, to form a so-called "coupon." The coupon is bent in a jig at approximately a 90.degree. angle. The leads are then bonded or laminated to a charge plate substrate, and the etchable material is removed.
In high resolution printhead making interconnects from the charge plate to the charge driver electronics becomes problematic. Electrical connection to planar charge plate lead terminations pose a problem in that the contact pads are positioned in a dense pattern and it is difficult to make assured contact to all the pads with a multi-pad connector, such as those using anisotropic epoxy or elastomeric connectors as described in U.S. Pat. No. 5,459,500. While these connections have been effective for longer arrays or higher density arrays, the pressure which must be supplied to provide contact can produce bowing of the charge plate. As a result of the bowing, contact pads in the center of the connector can have insufficient pressure applied to ensure that contact is made. Solder connections also have problems as the solder connectors tend to form bridges between adjacent leads when the solder is reflowed over a planar circuit.
As discussed in co-pending, commonly assigned application Ser. No. 09/211,212, raised bump contacts on the mating flex cable can be used to provide connection to the charging electrodes with low clamping forces, minimizing the bow of the catcher and charge plate. In practice however it has been found that the fabrication of flex cables having the desired raised bump contacts, using the prior art methods such as those found in U.S. Pat. Nos. 5,364,277 and 5,307,561, are very difficult to fabricate at the desired resolutions.
A need has therefore been identified for an improved technique for electrical connection to ink jet charge plates.